Infrared sensor has been widely applied in many hygienic products such as automatic faucet, automatic flushing urinal, toilet flushing device, toilet seat with hot water jet, hand dryer, flush toilet with hot air fan, etc.
Most traditional infrared sensor use an active mode of infrared induction, namely infrared emitting device emitting infrared light of a certain wavelength, which will be reflected by human body, and then received by infrared receiving device, with determining the strength of the reflected signal, to realize automatic induction determination. However, for some substances of low reflectance to infrared light (such as black colored clothes, hair, etc), it is hard to achieve the automatic induction determination. After being reflected by these substances, only a small portion of the infrared light emitted by infrared emitting device will be received by infrared receiving device. Due to the insufficient strength of the reflected signal, it will lead to that the sensor can not determine whether there is a target, which may result in induction failure.
In order to solve the above induction failure problem that is associated with the traditional infrared induction hygienic products, the Position Sensitive Detector (PDS) has been introduced into the area of hygiene and bathroom automation. As shown in FIG. 9, PSD is an optoelectronic device sensitive to incident light position. That is to say, when the incident light shines one different positions of a device's photosensitive surface, the PSD will output different electrical signals accordingly. The PSD achieves the automatic induction determination based on the principle of triangulation with the characteristic of an accurate distance measurement. As shown in the FIG. 9, after being focused by the Lens L1, light from a light source will be projected to the surface of the object to be detected. The reflected light is next focused by the Lens L2 to a one-dimensional PSD, and forms a light spot. If the center distance between the lenses L1 and L2 is b, the distance between the Lens L2 and the PSD surface (i.e., the focal length of the Lens L2) is f, the distance between the light spot focused on PSD surface and the center of the Lens L2 is x, then based on the nature of the similar triangles PAB and BCD, it can be drawn that the detected distance DIS is: DIS=bf/x. Hence, as long as the value of the light spot position's coordinate x has been determined, the distance of the target can be obtained.
When the detected distance of the target is within the pre-determined range, the distance detecting induction device will control the hygienic product to conduct such working states as watering, flushing and so on. Since the distance detecting induction device achieves the purpose of automatic induction by detecting the distance between target and the distance detecting induction device, rather than by determining the strength of the emitted signal, it thus can effectively solve the defect problem of “an insufficient strength of the reflected signal leads to an induction failure” that is associated with the traditional infrared induction.
However, with using such distance detecting induction device, it can be easily affected by the halo of the emitted infrared light, and hence results in certain problems of detection accuracy.